DESCRIPTION:(adapted from applicant?s abstract) Current theories of basal ganglia function hold that the striatum is the primary target of cortical input and that striatal information is conveyed to output structures via two pathways. The components of one pathway, the globus pallidus (GP) and subthalamic nucleus (STN), are thought to act as a passive relay for striatal information. However, evidence demonstrating cortical projections to STN suggests that it acts as a second input center, while reciprocal connections between STN and GP form an oscillator that may play an important role in the processing of cortical information. Little research exists, however, concerning STN function in freely moving animals. The experiments proposed here will assess movement-related activity and its modulation by dopaminergic drugs and behavioral context. Following surgical implantation of microwire bundles allowing single-unit recording from STN, rats will undergo four days of recording during acquisition of one of two versions (contexts) of an operant nosepoke-for-sucrose task. Rats will further undergo a fifth day of recording in which they are allowed free exploration of an open-field arena; during these experiments, behavior will be analyzed and correlated with STN activity; in addition, rats will be administered selective D1 or D2 dopamine receptor agonists, and the electrophysiological responses to these agonists will be examined and compared to predrug activity. Taken together, these results will provide a wealth of information concerning the nature of STN activity under different behavioral paradigms. This information will prove useful not only in understanding information processing within the basal ganglia, but may help to provide more effective treatments for psychomotor pathologies involving the basal ganglia.